greybus: audio: Add id to identify data connection

Added id field to data connection struct. This is used to identify which
data connection to use while enabling interface between module & APB.

Signed-off-by: Vaibhav Agarwal <vaibhav.agarwal@linaro.org>
Reviewed-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>